The present disclosure relates to a pressure-sensitive safety device for monitoring a technical installation comprising a sensor which has at least one first sensor cell and one second sensor cell and a first, a second and a third electrode for making contact with the first and the second sensor cell.
Owing to advances in signal detection and primarily electronic signal processing, the degree of automation of manufacturing processes has continuously increased over the years. Nevertheless, manual intervention is and remains an important part of a manufacturing process, and therefore development in recent years has been concentrated more on optimizing cooperation between a human and a machine. In particular, someone must not be put at risk during cooperation between human and machine. Therefore, a machine has to be able to observe its environment in its operating region and identify whether an object or a person is in the immediate vicinity. In addition to an extensive sensor system with which the machine observes its surrounding area, fault-free and reliable evaluation of these detected signals is also required in order to allow safe hand-in-hand operation between human and machine.
A sensor with which access to a machine or contact with the machine can be identified is disclosed, for example, in EP 2 528 234 B1. EP 2 528 234 B1 describes a tactile sensor of large surface area which is realized by connecting up a large number of individual sensor cells which, in the event of mechanical loading, change their electrical property in a defined manner. The sensor cells can be contacted individually by means of electrodes which are arranged in columns and rows, in order to determine a pressure distribution over the entire surface area from the changes in the individual cells. The sensor can be used as a safety shut-off mat in an access region to a machine or it can be arranged on the surface of a machine as artificial skin in order to identify collisions between a human and the machine or an object. The general principles and requirements in respect of design and testing for pressure-sensitive safety devices of this kind are defined in EN ISO 13856-1. In particular, the minimum safety requirements in respect of performance, marking and documentation are specified in the standard.
The greater the number of sensor cells to be interconnected, the greater the local resolution of the sensor, but also the greater the complexity of signal evaluation. Usually, a relatively large number of sensor cells are not evaluated at the same time and in parallel, but rather sequentially, that is to say the individual sensor cells are tested by an evaluation unit continuously one after another. However, this requires at least one further element for sequentialization in the signal processing chain, as a result of which the complexity of signal processing in the sensor and, necessarily, the number of potential sources of error increase.
DE 10 2012 203 670 A1 discloses a circuit arrangement which allows independent monitoring of a sequentialization element. The circuit arrangement is integrated in the sequentialization element and carries out a comprehensive self-test of the sequentialization element. The self-test can be performed continuously at intervals or can be initiated by a superordinate control unit as required. The result of the test is passed to a superordinate control unit or displayed to the user. The solution allows comprehensive protection against faults within the sequentialization element or the addressing of said sequentialization element, but requires sequentialization elements which are of highly complex construction and are therefore also expensive.